Elevated levels of ultraviolet (UV) irradiation, whether caused by sunlight or tanning ultraviolet devices, has the adverse effect of increasing the probability of skin cancer, other diseases of the skin as well as skin aging. Knowing when to seek for cover from ultraviolet radiation or when to apply or reapply sunscreen lotion is thus of importance.
UV responsive photochromic organic molecules that change color upon UV exposure can be used. Currently, there are such devices as UV indicator bracelets and cards that can be used to indicate the level of solar UV radiation. These are based on organic molecules such as spiro-oxazines, spiropyrans, fulgides, fulgimides, bisimidazoles and viologen derivatives. Usually, the color from these materials fades when UV exposure is removed, thus making them reusable indicators, but some of them are for single use. However, many of the reusable photochromic molecules have a short lifetime, and they can thus lose their functionality after too long or too intense UV exposure. Spiro-oxazines, however, may last for two to three years. The drawback for the spiro-oxazines is their high price. The high prices and short lifetimes decrease the usability of these materials in the photochromic UV indicator devices.
The inventors have therefore recognized a need for a low-cost ultraviolet radiation sensing material that is stable for a long period of time.